/***************************************************************************
 * libs/libc/misc/lib_crc8ccitt.c
 *
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.  The
 * ASF licenses this file to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance with the
 * License.  You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.  See the
 * License for the specific language governing permissions and limitations
 * under the License.
 *
 ***************************************************************************/

/* Public domain implementation: https://3dbrew.org/wiki/CRC-8-CCITT */

/***************************************************************************
 * Included Files
 ***************************************************************************/

#include <sys/types.h>
#include <stdint.h>
#include <crc8.h>

/***************************************************************************
 * Private Data
 ***************************************************************************/

static const uint8_t crc8_tab[256] =
{
  0x00, 0x07, 0x0e, 0x09, 0x1c, 0x1b, 0x12, 0x15,
  0x38, 0x3f, 0x36, 0x31, 0x24, 0x23, 0x2a, 0x2d,
  0x70, 0x77, 0x7e, 0x79, 0x6c, 0x6b, 0x62, 0x65,
  0x48, 0x4f, 0x46, 0x41, 0x54, 0x53, 0x5a, 0x5d,
  0xe0, 0xe7, 0xee, 0xe9, 0xfc, 0xfb, 0xf2, 0xf5,
  0xd8, 0xdf, 0xd6, 0xd1, 0xc4, 0xc3, 0xca, 0xcd,
  0x90, 0x97, 0x9e, 0x99, 0x8c, 0x8b, 0x82, 0x85,
  0xa8, 0xaf, 0xa6, 0xa1, 0xb4, 0xb3, 0xba, 0xbd,
  0xc7, 0xc0, 0xc9, 0xce, 0xdb, 0xdc, 0xd5, 0xd2,
  0xff, 0xf8, 0xf1, 0xf6, 0xe3, 0xe4, 0xed, 0xea,
  0xb7, 0xb0, 0xb9, 0xbe, 0xab, 0xac, 0xa5, 0xa2,
  0x8f, 0x88, 0x81, 0x86, 0x93, 0x94, 0x9d, 0x9a,
  0x27, 0x20, 0x29, 0x2e, 0x3b, 0x3c, 0x35, 0x32,
  0x1f, 0x18, 0x11, 0x16, 0x03, 0x04, 0x0d, 0x0a,
  0x57, 0x50, 0x59, 0x5e, 0x4b, 0x4c, 0x45, 0x42,
  0x6f, 0x68, 0x61, 0x66, 0x73, 0x74, 0x7d, 0x7a,
  0x89, 0x8e, 0x87, 0x80, 0x95, 0x92, 0x9b, 0x9c,
  0xb1, 0xb6, 0xbf, 0xb8, 0xad, 0xaa, 0xa3, 0xa4,
  0xf9, 0xfe, 0xf7, 0xf0, 0xe5, 0xe2, 0xeb, 0xec,
  0xc1, 0xc6, 0xcf, 0xc8, 0xdd, 0xda, 0xd3, 0xd4,
  0x69, 0x6e, 0x67, 0x60, 0x75, 0x72, 0x7b, 0x7c,
  0x51, 0x56, 0x5f, 0x58, 0x4d, 0x4a, 0x43, 0x44,
  0x19, 0x1e, 0x17, 0x10, 0x05, 0x02, 0x0b, 0x0c,
  0x21, 0x26, 0x2f, 0x28, 0x3d, 0x3a, 0x33, 0x34,
  0x4e, 0x49, 0x40, 0x47, 0x52, 0x55, 0x5c, 0x5b,
  0x76, 0x71, 0x78, 0x7f, 0x6a, 0x6d, 0x64, 0x63,
  0x3e, 0x39, 0x30, 0x37, 0x22, 0x25, 0x2c, 0x2b,
  0x06, 0x01, 0x08, 0x0f, 0x1a, 0x1d, 0x14, 0x13,
  0xae, 0xa9, 0xa0, 0xa7, 0xb2, 0xb5, 0xbc, 0xbb,
  0x96, 0x91, 0x98, 0x9f, 0x8a, 0x8d, 0x84, 0x83,
  0xde, 0xd9, 0xd0, 0xd7, 0xc2, 0xc5, 0xcc, 0xcb,
  0xe6, 0xe1, 0xe8, 0xef, 0xfa, 0xfd, 0xf4, 0xf3
};

/***************************************************************************
 * Public Functions
 ***************************************************************************/

/***************************************************************************
 * Name: crc8ccitt
 *
 * Description:
 *   Continue CRC calculation on a part of the buffer.
 *
 ***************************************************************************/

uint8_t crc8ccittpart(FAR const uint8_t *src, size_t len, uint8_t crc8val)
{
  uint8_t *pos = (uint8_t *) src;
  uint8_t *end = pos + len;

  while (pos < end)
    {
      crc8val = crc8_tab[crc8val ^ *pos];
      pos++;
    }

  return crc8val;
}

/***************************************************************************
 * Name: crc8ccitt
 *
 * Description:
 *   Return a 8-bit CRC of the contents of the 'src' buffer, length 'len
 *   using a CRC with the polynomial x^8+x^2+x^1+1 ("0x07" polynomial).
 *
 ***************************************************************************/

uint8_t crc8ccitt(FAR const uint8_t *src, size_t len)
{
  return crc8ccittpart(src, len, 0);
}
